Re: 7B80 sweeping off the screen

Roger Evans


Thank you for that particular insight, my suggestion was just to have a single plugin (the 7B80) in the 7603 and move it to whichever slot gave best access for probing. Your suggestion is much better since you are using the working parts of the 7603 to diagnose the part which is not working. I have previously suggested that if you have one channel not working on a normal double channel (not mainframe plus plugins) scope you can use the working channel to probe the non working channel from the input connectors as far as the channel switch.


Re: Looking for P7001 / GPIB ROM images

Holger Lübben

Hi Raymond,

Thanks for your help.

My board and ROM layout matches your description.
Here is a picture of my board:
As you can see someone changed some of the ROMs in the past - maybe thats the source of my problems.

It would be nice to get the files in "plain binary format" (*.bin), but I can reformat nearly every format.


Re: Looking for P7001 / GPIB ROM images


On Sat, May 23, 2020 at 02:12 PM, Holger Lübben wrote:

Is there anybody with a P7001/GPIB combo in this group who could provide me
with working copy of the ROM files?
Hi Holger,
I may have a way to read the ROMs in my unit.
Just to verify we're talking about the same hw/fw versions: My interface (board 670-4882-03) contains 7 pcs. 2708, numbered 160-0174-00.. 160-0810 in ink handwriting. Also, they all have "37-78" written on them in pencil. Could be a date code.
If these are what you're looking for, what format should the ROM code files preferably be in (Intel, Motorola, Tek, TI)?


Re: 7B80 sweeping off the screen

Albert Otten

On Sat, May 23, 2020 at 12:42 PM, <ik1zyw@...> wrote:

First of all, on the "+ sawtooth" output in the back of the mainframe, the
working 7B53A produces a down sloping negative signal, sweeping between -4.5V
(trace @left) and -5.5V (trace @right). Measured on the low-ish impedance
analog voltmeter.

OTOH the 7B80 produces an up going positive "+ sawtooth" signal between +1V
(theoretical left) and +10V (theoretical right). Its frequency follows
time/div changes. Trigger is honoured (no sweep in single-shot for example).

Which reading is correct?
Hi Paolo,

The 7B80 reading is correct. If you change the Hor Pos control you might notice that the signal is actually between 0 V and +10 V. Just checked this in my similar 7633 (with 7B80 and 7B53A) and the Calibration procedure also mentions that 10 V amplitude.

In addition to Roger's comments (if this is not already what he meant), note that you might also use the 7603 as ordinary 'scope with 7B80 in the Left bay and some 7A in the middle bay and the 7B53A as time base. Trigger the 7B80 externally with some Line frequency signal and set the 7B53A also for Line triggering. Now you can probe the 7B80 internal circuitry and display wave forms via the 7A module. (Of course this makes it impossible to probe the rhs of the 7B80 though.)



Re: 475 questions

Michael W. Lynch


No worries about not responding personally to my post. You have been inundated with advice and in my experience with this forum, most people do not expect a personal reply for every piece of advice they offer.

As for desoldering tools you will not be sorry for the route you have taken. I did the same thing when I got started in this hobby almost 3 years ago. You are spot on about the heat, I did not mean to discourage the use of the Weller method, Just cautioning about too much heat for too long a period. You see to have that figured out. I have a Weller for those "Big" jobs as well.

With the powered desolder station, you can use the iron of choice to apply quick heat (supplementing the desolder pump heat) and suck the solder up quickly. Quicker is better. No need to rush, The first cap will take longer and you will gain proficiency as you do each subsequent cap.

For those "hole fillers". using a piece of 3/8" brass rod, I machined a small brass bushing with a 1/16 hole in the center. OD is then turned to just fit into the large holes vacated by the ground lugs on the caps and with a thin flange or "brim" on one side (the result looks like an old fashioned straw hat only with a small hole where the wearers head would go.). Drop these into the 3 big holes in the board for each cap and solder into place. Now you have a 1/16" hole for the little pins of those boards to solder into, instead of trying to fill that huge hole with solder. I wish now that I had taken pictures of what I did. It worked very well for me. I am sure that there are many efficient methods to accomplish this, I just had the time and the lathe available to do what I did. Once you get it apart, you will see what I mean and come up with some suitable method to accomplish the task.

One piece of advice that I will offer is to get into a systematic method of diagnosis, don't be tempted to "Shotgun" the task. You are started in the correct place, the main LV power supply. This is common to almost any instrument that you will encounter, going forward. Get all the power supplies working before you try to "Fix" any other problems.

I found the 465 manual P/N 070-1861-00 has an excellent troubleshooting section and is almost identical to the 475. If nothing else, this section can give you an idea of the flow of the power and how to work systematically to isolate the various supplies and locate your shorts or excess loads. You will find that certain manuals for certain instruments do a better job of explaining a particular portion of the circuit than others. The nice thing about the 465/465B 475, 475A and other derivatives is that they are all very similar, so you might glean some insight by looking at a similar section of a different instrument manual in the series (if that makes any sense).

When digging into a problem, spend a lot of time understanding the "Theory of Operation" or "Circuit Description" Section of the applicable manual, this is you best resource. This section cuts through the complexity of the circuit and the schematic diagram. This section is the "Cliff Notes" version, if you will, and directs you to the primary operations or critical components of each circuit.

Ask lots of questions and carefully consider all advice. People in this group are eager to help, you will find no better resource for your project.

Finally, Keep at it, I was where you were just s few short years ago, no previous experience in this sort of electronics, just the desire to learn and time to do so. .

Best of luck in your journey.

Michael Lynch
Dardanelle, Arkansas

Update on my 7854 diagnostics project

Holger Lübben


As promised an update about my 7854 diagnostics project:

I've finished all tests with my ROM card replacement. After that I've tweaked the layout a little bit and ordered a final sample.
These are pictures of the earlier prototypes:

ROM card:

Keyboard-overlay card:

Last week a good friend borrowed me his MicroLab. So at the moment I have a (nearly) complete 7854 digital diagnostics sytsem at home.
Pictures of the system can be found on Tekwiki:

I've also uploaded the bin files.

Next step is to analyze and understand the system in detail.


Looking for P7001 / GPIB ROM images

Holger Lübben


The GPIB interface in my P7001 does not work correctly. I did some debugging and I'm pretty sure the error is in the firmware.
Is there anybody with a P7001/GPIB combo in this group who could provide me with working copy of the ROM files?

The files on Tekwiki come from the ROMs in my device - so they are also buggy.



Re: Tek 7K flex extenders available again


HI John,

I am very interesting to buy the 7k flex extender so plese tell me the cost included the shipping at this address :

COLISEXPAT - ref.276174
10, rue Eugène Hénaff
93000 - BOBIGNY
tel: Mob :

I will pay by PAYPAL or AMEX card

Thank you for answer.


Re: 7B80 sweeping off the screen

Roger Evans

You can operate the 7B80 in any of the three slots of the 7603 and it will drive the vertical deflection if you put it in a vertical slot. So if you insert only the 7B80 and take all side panels off both the mainframe and the plugin you have some options for probing but you will need to run in auto trigger mode to have the time base sweeping with no trigger. If you don't have a second scope but do have an analogue multimeter you can run on the slowest possible sweep speed and the voltages should largely follow what is in the manual but obviously on a slower timescale.

If you probe test point TP345 (waveform 4) you can confirm that the sweep generator is producing the correct sweep voltage range and polarity. Measuring the waveform at the collectors of Q448 and Q458 (waveforms 8 and 9) you should see if either half of the paraphase amplifier is causing the problem. Then you need to follow the signal through Q428 etc to track down the culprit. If the transistors are socketed ( mine aren't) I would just begin by testing Q424, Q428, Q434, Q438.



7B80 sweeping off the screen


My R7603 mainframe came with a non-functional 7B80 plug-in. Back then I bought a 7B53A and happily used the scope until few weeks ago when I came across the 7B80: time to fix it, or find a new home. I am asking for guidance because it doesn't seem too broken: it triggers, but no trace is drawn on the visible area of the screen. I have no other oscilloscope, only analog and digital multimeters. Frequency counter, signal generator and VNA won't be useful in this mission.

First of all, on the "+ sawtooth" output in the back of the mainframe, the working 7B53A produces a down sloping negative signal, sweeping between -4.5V (trace @left) and -5.5V (trace @right). Measured on the low-ish impedance analog voltmeter.

OTOH the 7B80 produces an up going positive "+ sawtooth" signal between +1V (theoretical left) and +10V (theoretical right). Its frequency follows time/div changes. Trigger is honoured (no sweep in single-shot for example).

Which reading is correct?

If I turn CRT intensity to the max I see the green halo coming from the right and it flashes off when the beam is swept back. In these conditions, pressing the "Position" button shows the cursor leaving a trace entering from the RHS of the CRT and a dot is positioned a couple of divisions right of the timing value compressed position. So the beam is trying to sweep somewhere behind the second vertical plug-in bay :)

I have run the 7B80 base without Q344 and Q346, therefore having the sweep signal (TP345) pass through R343 and off to "+ sawtooth" output. The result is a negative sloping signal between -2V and -3.5V on the "+ sawtooth" output, so much closer to 7B53A's values, but not enough to see a trace.

So far I have tested Q344 (hFE~=50), Q346 (hFE~=50), Q458, U416, all apparently good.
Not owning a plug-in extender I found a trick to measure voltages inside the 7B80 in-place, and +50V, +5V and -15V picked near Q344/Q346 stage measure OK, few 10's of mV low and no sign of AC.

Why on Earth do I get a reverse and amplified sweep?! If voltages were somehow reversed the whole plug-in would be totally dead. Or the 7B80 isn't meant for a 7603 mainframe?!

Simply put: help!

DC508A Option 7 installation guide

Nenad Filipovic

Hi Group,

With big thanks to Dennis Tillman I became owner of a DC508A counter intended for my 7L13/TR502 combo. Installation of the required Option 7 upgrade for the counter is not difficult, but some steps are poorly documented and error prone, or scattered in different documents. To resolve this I compiled a set of resources to help with this upgrade:

The above documents and the following instructions should contain all info that you need to complete the Option 7 upgrade.

1. The provided Tekscope article "Tekscope_Vol07_Num5-1_TR_502_Tracking_Generator.pdf" describes the principles of operation of the whole spectrum analyzer - tracking generator - counter combo.

2. TM503 mainframe is recommended to house the TR502 and the counter, however you can also use the larger mainframes. Designated slots must be used for the two, and wired (at the back side of the mainframe motherboard) according to the "TM503_TR502_DC508A_Wiring_Information.pdf" document. Pins denoted on page 19-5 should be interconnected between the counter and the tracking generator (same pins on both).

3. Tracking generator and spectrum analyzer should be connected by a proprietary LEMO connector cable (wiring description in "012-0648-00_TR-502_LEMO_cable .pdf"). As mentioned in this document the original cable is way oversized (stiff for use and difficult to solder). My recommendation would be LiYCY 6x0.14 mm² (26AWG) or equivalent (cable diameter of 4.5-5mm). The LEMO connector (2pc required) part number is FFA.1S.306.CLAC52 (for cables up to 5.2mm thickness, check LEMO product catalog).

4. Tracking generator and counter should be connected by a 50Ohm SMA to BNC short pigtail cable (any decent RF type would do). Example can be seen in any of the operation demonstration photos included.

5. DC508A main PCB has a smaller daughterboard attached to its back side, where components need to be added:
- 74LS76
- 7404
- 7401 (2pcs)
- resistors (3x1kOhm, 2x5.1kOhm)
- 100nF ceramic capacitor
- 18pin standard (100mils pitch) right angled header
Schematic and layout are in the DC508A service manual (the provided manual "DC508A Instruction Manual 1982.pdf" is not OCRed, but contains uncut high-res schematics), and the assembled board can be seen on the "DC508A_Option_7_-_3_-_Daughter_PCB_Connected.jpg" photo.

6. Two wired connectors (10pin and 8pin) are required for the above mentioned PCB extension. The recommended placement and wire routing can be seen on the "DC508A_Option_7_-_2_-_Connector_Wiring.jpg" photo. Header pins are marked by single letters on the PCB, please see the next point regarding wire connections.

7. Before soldering the connector wires, some jumpers need to be removed and added to the DC508A main PCB. All this info is scattered throughout the service manual schematics, and hunting it all down is incredibly annoying and error prone. Please refer to "DC508A_Option_7_-_1_-_Installation_Map.jpg" for jumper modifications and soldering points for connector wires. The map points slightly differ from the letter markings on the back of the DC508A main PCB, but are electrically equivalent (chosen for soldering convenience).

8. Simple operation demonstration can be seen on the three photos included (FM broadcast band and RF signal from TV pattern generator). Performance specs can be found in the Options chapter of the service manual on page 6-1 (40). For spans of 100kHz/div and wider the count resolution is always 100kHz. Spectrum analyzer needs to be well settled thermally for center frequency stability, and even then it may struggle to maintain this 0.1MHz precision. In phase locked modes (spans of 50kHz and narrower) the count resolution is increased, and can be additionally selected using counter's own resolution control. This resolution will affect the time it takes to complete the count, effectively limiting the sweep speed of the spectrum analyzer. Center frequency stability is more-less decent for an instrument of this age.

9. Factory standard Option 7 includes Option 1 - OCXO. This option is not mandatory for primary functions of the Option 7 upgrade.

Hope these instructions help,
Best regards,
Nenad Filipovic

Re: Questions I have if Attachments are Permitted

John Parkins G8KVP


Or if you don't want attachments you can just turn them off. Easy.

Saturday, May 23, 2020, 7:40:18 AM, you wrote:

s> Again,

s> How difficult can it be?

s> Put relevant pictures in a TekScopes album;

s> Put link to album in your topic message;

s> Result:

s> No unwanted attachments,

s> so no forced bandwidth usage,

s> Relation between topic and pictures is preserved.

s> Problem solved. ( At least in my world)

s> Leo


Best regards,
John mailto:john@...

Re: 475 questions


Bruce, I can see you are bursting with enthusiasm to get your 475 'on the air' but are hampered somewhat by lack of electronics knowledge.  Keep at it!  There are lots of tutorials out there on the big bad web so go find some that you find easy to digest and keep asking questions.  Lots of questions!

I don't have a 475 but I have downloaded a service manual to see what the power supply looks like and it seems very straightforward. I see a conventional mains transformer (T1400) with multiple separate secondary windings for the different DC voltages, each with a full-wave rectifier, filter cap and then a conventional series regulator.  Any one of the full-wave rectifiers, or filter capacitors, could be faulty but there could be other faults too.

Looking back on this thread I think you satisfied yourself that the 'scope was safe to operate on full mains voltage after you did the incandescent bulb test and nothing bad happened.  Correct?  And then you reported "After seeing no ill effects, but all voltage readings low, I shut it off  ... "  What DC voltages do you measure across the unreg filter caps C1414, C1442, C1452, C1462 and C1472?  These unreg DC voltages should be somewhat above the intended regulated output voltage so that the regulator transistors can regulate the final output voltage.

There will also be some 120Hz AC ripple voltage on these unreg filter capacitors as Dave mentioned earlier - that's not a bad thing if the ripple is small, it shows that the caps are doing their job. There might be a tiny bit of AC ripple on the regulated DC output but it should be very small as the regulator should stop it.  To explain how a full wave rectifier works, look at the +15V circuit where the transformer secondary (17, 18)  feeds rectifier CR1442 and then unreg filter cap C1442.  Think of each diode in the rectifier as a one-way valve: when the instantaneous voltage at (17) of the secondary winding is positive WRT (18) then the 'top' diode and the 'bottom' diode will conduct to charge up C1442 with the polarity as shown.  On the next half cycle of the AC mains, transformer (18) will be positive WRT transformer (17) and the other two diodes will conduct, charging up C1442 with the same DC polarity.   And when not actually being charged, the voltage on C1442 will drop as current is (or should be!) flowing out to the parts of the 'scope which run on unreg +15V and regulated +15V DC supplies.  So the filter cap is a 'storage tank' of charge, topped up 120 times per second and its voltage will drop a little between charging pulses with this voltage variation known as an AC 'ripple' voltage on the capacitor.  If a capacitor goes faulty with high ESR or loss of capacitance then the ripple will be higher than intended and that needs investigating altho' high ripple can have other causes.

But as others have said, there could be a variety of faults in your eqpt and a methodical approach will find them, eventually.  I'd recommend the methodical approach rather than just replacing suspect components unless you can see a distorted/cooked/sick component which obviously needs replacing.  Brown patches on circuit board are long-term heat damage; some is normal in old eqpt tho'.

I'd suggest that you measure the voltage of the reg +50V at the test point (as it's a ref for the other DC supplies) and the DC voltage *and* AC voltage across each of the unreg filter caps (C1414, C1442, C1452, C1462 and C1472) and post your readings to this group and see what the collective wisdom of ~8000 Tektronix enthusiasts can bring.

And on a slightly different theme: if you have a camera which can see infra-red then have look at the power supply circuit when it's operating.  A few warm components is normal but any component which is getting hot should stand out and that might lead you to something worth investigating further.

Down under.

On 23/05/2020 2:56 pm, ciclista41 via wrote:
Thanks, Dave!

I'm surprised that I would find AC voltage at the rectifier filter caps. I thought those came after the rectifier in the circuit, so any AC would be gone by that point. And if the rectifier IS shorted, THEN I would expect to see AC at the caps. Clearly, I have much more to learn about power supply circuitry.

I will try these tests and see what I find.

Thanks for your help!


This email has been checked for viruses by Avast antivirus software.

Re: Questions I have if Attachments are Permitted



How difficult can it be?

Put relevant pictures in a TekScopes album;

Put link to album in your topic message;


No unwanted attachments,

so no forced bandwidth usage,

Relation between topic and pictures is preserved.

Problem solved. ( At least in my world)


Re: 475 questions


Hi Michael!

Reading back through the thread just now, I realized that I never replied to your helpful post. So sorry! Just because I'm retired, doesn't mean I don't get interrupted occasionally. I haven't made any progress other than replying to posters today due to an overnight visit from my not-quite 3-year-old granddaughter. She's a wonderful distraction! The scope can wait when she's around.

I just ordered a powered desoldering gun after some frustration with my spring-loaded one. I had never used either before, so didn't know what I could achieve with the spring. It didn't seem too bad, and probably will work fine on a single-sided board, or perhaps with this board for certain components, but the big caps and their associated ground lugs present more of a challenge. After watching the powered ones being demonstrated on YouTube, I don't think I'll regret the purchase. I have used rosin core solder quite often in the past, but never had flux on its own except in plumbing, and one doesn't get far with solder wick without flux. If the desoldering gun won't do the trick, the flux and wick will have to.

As far as heat goes, my impression is that quite a bit over a short duration is preferred over too little heat over a longer duration or too much heat, period. Also, the Weller with stock tips is much cooler than the #14 copper wire, if Mr. Carlson's example is instructive. I've only used the Weller in soldering since I got it as a gift back in my 20's until I got the Yihua recently. I did get a cheap 20W for a more delicate project that I never used again. In retrospect, I probably wasn't using it properly. When I do copper plumbing, I use propane or MAP, but that's a different kettle of fish. So, I'm going to try to use the Yihua and resort to the Weller if I need more heat. It does take more when there's more thermal mass to heat up, as seems to be the case with the lugs associated with the PS caps. The flux should arrive tomorrow.

You and one other have suggested the round PCB's. Thanks for the Ebay listing! I'm going to take a look at my options after getting the caps out and being able to see what I'm dealing with. Probably will go that route, though. Also like your idea of reinforcing the through-holes with brass ferrules. Do you flare the ends, or just solder some appropriate diameter brass tubing in there?



Re: 475 questions


Hi John!

That's a great story and endorsement of this forum and its denizens! I certainly don't have the sentimental value to my 475 that you have to yours. So sorry for your loss--my folks are gone, too.

However, I expect my scope to acquire some sentimental value along the way as I put time, effort, and money into it. With supportive folks like you and Barry cheering me on, and the many who are contributing technical expertise and advice, my confidence is increasing my the day!

I'm actually taking on this new hobby partly because I have always felt that electronics was a bit beyond me. Now that I'm a retired high school math teacher, I have the time and inclination to prove myself wrong!


Re: 475 questions


Thanks, Dave!

I'm surprised that I would find AC voltage at the rectifier filter caps. I thought those came after the rectifier in the circuit, so any AC would be gone by that point. And if the rectifier IS shorted, THEN I would expect to see AC at the caps. Clearly, I have much more to learn about power supply circuitry.

I will try these tests and see what I find.

Thanks for your help!


Re: 475 questions


Hi Harvey,

So frustrating! I had a reply nearly as long as your post above, but accidentally hit some button and the entire thing evaporated. Oh well, maybe I will be less wordy and more to the point this time.

Thanks for such a thorough set of suggestions and explanations! This sort of advice is so valuable to me. I understood the part about the rectifiers right away. The part about the linear voltage regulators will take some research on my part to get up to speed on that. I think I almost understand the part about NPN emitter followers, though. I'll be using all of that as well as everyone else's advice as I figure this thing out. Glad the advice has not been conflicting! Gives me confidence that I'm headed in the right direction.

So, tacking a question on to this reply that's meant for anyone following the thread, since you've spent so much time already:

How do I know what generic components are best to replace the original parts? For instance, the tantalum caps come up a lot, but I assume when folks replace them, they don't use the same as the originals. What DO they use? There are so many types of capacitor, even in this one scope, and it's more than 37 years old. The large power supply caps are replaced with newer, smaller electrolytics, but I've heard that some brands are more reliable and last longer than others. What are some good choices?

I looked up one of the original rectifiers, an MDA960-3. I found a NOS of it on Ebay for almost $9 plus shipping. At that rate, this is going to get expensive very quickly. So what can I use instead? I assume that by looking up the specs on each original component that I end up replacing and finding something that meets or exceeds those specs, I'll probably be okay, but I could really use the voice of experience here.

I'm aware of Digikey and Mouser. I ordered some diodes from Digikey several years ago to build a rectifier that I used to convert the power from a hub generator on my touring bike to charge my phone as I rode. It even worked, although my buddy said the one I built for him killed his phone. Mine had some issues that I never resolved. I'm hoping to soon have the ability to design my own circuit, rather than copying someone else's, and have it be rock-solid! But, I digress...

Thanks again, Harvey!


Re: Questions I have if Attachments are Permitted

John Griessen

On 5/22/20 4:55 PM, JJ wrote:
one issue I found was that the photos in the galleries aren't back
linked to the thread - so you basically have interesting photos with no
discussion. That is, it's a bit disappointing to browse the images, find
something interesting and then be unable to put the image in context with
the thread from where it was referenced.
You've hit on one of the pros for attachments -- easy quick inclusion of images inline
linked to the text like the www. Most chat methods that include this are forums that require a
login active to do anything, so are similar to providing independent photos on a server, except the forum software manages the creation in reduced file size of images and links them.

For this case there is no image linking to emails.

Wouldn't it be nice if there was a way could enable that? Many of us already have to do a login to to read mails anyway...

I send images to my server and publish links to that, but it may go away in a few years like many of the imgur, bitbucket, photobucket, flickr, dropbox, etc. photos do.

Re: Questions I have if Attachments are Permitted


Hi JJ,
It was nice seeing you at the meeting the other night.

I never gave this any thought until you brought it up just now. You are correct. The person uploading the pictures doesn't have to say anything at all about what the photos are, why they are there, when they were put there, or who put them there. That is a drawback.


-----Original Message-----
From: [] On Behalf Of JJ
Sent: Friday, May 22, 2020 2:55 PM
Subject: Re: [TekScopes] Questions I have if Attachments are Permitted

I haven't followed the attachments argument this time around - it comes up once per year and it's always the same questions, answers and end result.
But, one issue I found was that the photos in the galleries aren't back linked to the thread - so you basically have interesting photos with no discussion. That is, it's a bit disappointing to browse the images, find something interesting and then be unable to put the image in context with the thread from where it was referenced.
Has this changed or am I just not using it correctly?


Dennis Tillman W7pF
TekScopes Moderator